As influenzas go, the H7N9 virus at first seemed relatively benign: in late March, the Chinese government reported that three individuals had contracted the illness, and that two had died. The disturbing revelation was tempered, however, by reassurances that human-to-human transmission was highly unlikely, and that Chinese health authorities were taking unprecedented measures to monitor and contain the virus. But four weeks later, the situation has changed: 23 people are now dead, and 122 have been infected across several provinces. Officials with the World Health Organization last week warned that the virus is one of "the most lethal" they've ever seen, and appears to jump easily from birds to humans.
The progression of this virus, it appears, is still far from over. And experts already warn that bird-borne viruses like H7N9 will continue to emerge from China for the foreseeable future — largely because of a unique combination of ecological and cultural factors that make the country a hotbed for deadly avian influenzas.
For the rest of the story: http://www.theverge.com/2013/4/29/4281702/why-did-the-new-h7n9-outbreak-start-in-china